Enhanced oil recovery (EOR) processes employ thermal energy to facilitate the recovery of oil, particularly heavy oil, from oil-bearing formations. One particular process widely used in Canada for recovering heavy oil is referred to as steam assisted gravity drainage (SAGD). In a SAGD process, steam is injected into the oil-bearing formation. Generally, several tons of steam is required for each ton of oil recovered. In this process, steam heats the oil in the oil-bearing formation and this reduces the viscosity of the oil and facilitates the flow of oil to a collection area. In this process, however, steam condenses and mixes with the oil to form an oil-water mixture. The mixture of oil and water is pumped to the surface and oil is separated from the water by conventional processes that form what is referred to as produced water.
In some SAGD processes, evaporators are used. They evaporate produced water and produce a distillate that is directed to a steam generator that produces steam that is injected into an oil-bearing formation. The steam injected into the oil-bearing formation facilitates the removal of oil from the formation. Evaporators also produce a blowdown. In many cases, evaporator blowdown is not suitable for disposal by deep well injection. This means that the evaporator blowdown must be further concentrated before disposal. It is known to use conventional crystallizers to concentrate evaporator blowdown. Generally the maximum concentration of evaporator blowdown in conventional crystallizers is on the order of 55-60% total solids (TS). The total solids concentration achievable by conventional crystallizers in SAGD processes is limited by the viscosity of the blowdown, scaling and the energy required to evaporate the blowdown. The lower the concentration total solids in the treated evaporator blowdown, the greater the disposal volumes and the higher the operating costs for the process.